The present invention relates to a booster as may be used in a brake of an automobile, and more particularly, to a valve mechanism of a booster.
A conventional booster generally comprises a valve body slidably disposed within a shell, a constant pressure chamber and a variable pressure chamber defined across a power piston secured to the valve body, and a valve mechanism disposed within the valve body to switch a flow path. The valve mechanism comprises an annular vacuum valve seat, a valve plunger slidably fitted into the valve body, an annular atmosphere valve seat formed on the valve plunger, a valve element adapted to be seated upon the vacuum valve seat and the atmosphere valve seat, a constant pressure passage communicating with a space radially outward of a vacuum valve where the vacuum valve seat is in contact with the valve element, an atmosphere passage communicating with a space located radially inward of an atmosphere valve where the atmosphere valve seat is in contact with the valve element, and a variable pressure passage communicating with a space located between the vacuum valve and the atmosphere valve.
When the booster constructed in the manner mentioned above is inoperative, the valve element is seated upon the atmosphere valve seat which is formed on the valve plunger to close the atmosphere valve, thus interrupting the communication between the atmosphere passage and the variable pressure passage while the valve element is removed from the vacuum valve seat to open the vacuum valve to allow the constant pressure passage to communicate with the variable pressure passage. Under this condition, the constant pressure chamber and the variable pressure chamber defined across the power piston of the booster communicate with each other through the constant pressure passage and the variable pressure passage, and accordingly, there is no pressure differential across the power piston and hence the valve body and the valve plunger remain at rest in their inoperative positions.
On the other hand, when the booster is actuated, the valve element becomes removed from the atmosphere valve seat which is formed on the valve plunger to open the atmosphere valve, thus allowing the atmosphere passage to communicate with the variable pressure passage while the valve element becomes seated upon the vacuum valve seat to close the vacuum valve to interrupt the communication between the constant pressure passage and the variable pressure passage. Under this condition, the variable pressure passage defined behind the power piston of the booster communicates with the atmosphere through the variable pressure passage and the atmosphere passage, whereby a pressure differential acts upon the power piston to drive the valve body forward.
The described booster performs a booster operation by operating the valve mechanism in a manner such that an input applied to a brake pedal and a reaction from a master cylinder is balanced. However, when a reaction from the master cylinder is small during an initial phase of operating the brake, a servo balance condition of the valve mechanism where the vacuum valve and the atmosphere valve are both closed becomes unstable, causing inconveniences such as developing oscillations and abnormal sounds.
Specifically, when the reaction from the master cylinder is small in magnitude, the force which acts in a direction to close the atmosphere valve is small, and thus the atmosphere valve cannot be instantly closed, allowing an excess of the atmosphere to be introduced into the variable pressure chamber. This results in opening the vacuum valve when the atmosphere valve is successfully closed as the valve mechanism subsequently tends to balance in response to the reaction from the master cylinder and the input from the brake pedal because the reaction is relatively large in proportion to the input.
This problem also relates to the master cylinder. For example, recently, there is a brake system in which a braking liquid from a reservoir is fed through a liquid pressure chamber of the master cylinder to develop a braking pressure when the master cylinder is not operated. In a design, such a brake system has a wide passage between the liquid pressure chamber of the master cylinder and the reservoir in order to allow the braking liquid to be fed rapidly from the reservoir.
With such a master cylinder, a liquid pressure cannot build up in the liquid pressure chamber until a piston which is linked to the booster interrupts the communication between the reservoir and the liquid pressure chamber. Accordingly, a reaction from the master cylinder is reduced during the initial phase of brake operation, causing the described inconveniences.
In view of the foregoing, it is an object of the present invention to provide a valve mechanism of a booster which prevents an excess of the atmosphere from being introduced into the variable pressure chamber during the initial phase of brake operation, thereby allowing the occurrence of oscillations or abnormal sounds to be prevented during the initial phase of operation of the valve mechanism.
Specifically, the present invention relates to a valve mechanism of a booster comprising a vacuum valve which opens or closes a communication between a constant pressure chamber and a variable pressure chamber defined across a power piston, and a first atmosphere valve which opens or closes a communication between the variable pressure chamber and the atmosphere. In accordance with the present invention, the valve mechanism also comprises a second atmosphere valve which is disposed nearer the atmosphere than the first atmosphere valve for opening or closing a communication between the first atmosphere valve and the atmosphere, and an orifice passage which allows a portion of the second atmosphere valve which is disposed nearer the first atmosphere valve to communicate with the atmosphere, the arrangement being such that when the booster is inoperative, both the first and the second atmosphere valve are closed to interrupt the communication between the variable pressure chamber and the atmosphere while when the booster is actuated, the first atmosphere valve is opened to allow the atmosphere to be introduced into the variable pressure chamber through the orifice passage and subsequently the second atmosphere valve opens to allow the atmosphere to be introduced into the variable pressure chamber through the second atmosphere valve together with the orifice passage.
With the described arrangement of the present invention, under the condition that the first atmosphere valve, which corresponds to the atmosphere valve of a conventional booster, is open, the variable pressure chamber is blocked from communication with the atmosphere by the second atmosphere valve which remains closed, but communicates with the atmosphere only through the orifice passage, which restricts the inflow of the atmosphere into the variable pressure chamber, thus reducing the amount of the atmosphere introduced into the variable pressure chamber in comparison to the conventional booster.
This allows an appropriate output to be obtained in response to an input during the initial phase of the brake operation, preventing a subsequent occurrence of oscillations of or abnormal sounds from the valve mechanism.
When a second seat on the valve element, which forms a second atmosphere valve, becomes removed from the first atmosphere valve on the valve plunger, the atmosphere can be rapidly introduced into the variable pressure chamber through the second atmosphere valve and the first atmosphere valve which is previously open, allowing the brake booster to operate in the similar manner as in the prior art.
Above and other objects, features and advantages of the present invention will become apparent from the following detailed description of several embodiments thereof with reference to the drawings.